Product injection apparatuses are, of course, well known for combining a first product such as a foaming agent with a primary fluid such as water. In fire fighting, for example, the use of a foaming agent is used to reduce the oxygen supply to the fire which hastens its termination.
Heretofore, product injection apparatuses used venturi pressure to draw a product from a reservoir into a primary fluid line. The system, however, worked well over only a limited venturi inlet range. Other apparatuses have not been able to quickly and efficiently switch between different products and the system must be shut down to replenish or substitute another product supply. Other apparatuses may be limited in the amount of product injected into the primary fluid and the pump may be of the fixed RPM type which does not allow increased product injection if the primary flow is increased. Other systems are unnecessarily complex with the result that field servicing may be difficult and, concomitantly, expensive.